Fibrosarcoma (FSA) in Dogs (Bone)

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Overview of Canine Bone Fibrosarcoma

Fibrosarcoma, commonly abbreviated as FSA, is a type of cancer that arises from the fibrous connective tissues of the skull, spine, pelvis and ribs but can arise from any bone that can occur in dogs. This cancer is a part of a group of tumors that would be termed non-osteosarcomas of bone and can sometimes be very difficult to distinguish from the far more common osteosarcoma. 

The cause of fibrosarcoma is largely unknown. It is a rare tumor in comparison to osteosarcoma. This cancer is seen most commonly in older male dogs, except for a certain variety that is seen in the mouths of younger dogs. Most commonly, it effects the bones of the spine, pelvis and skull but can less commonly effect the legs.

What to Watch For

Symptoms of bone cancer in dogs may include: 

  • Signs of lameness or pain especially in the legs
  • Unexplained swelling of any bones
  • Difficulty swallowing and eating
  • Bleeding from the mouth, and/or a bad mouth odor
  • Diagnosis of Fibrosarcoma of the Bone in Dogs

  • Complete physical exam
  • Radiographs (X-rays) of the affected body part
  • Radiographs of the chest/lungs
  • Complete blood cell count (CBC)
  • Biochemistry profile
  • Urinalysis
  • Biopsy of the tumor
  • Treatment of Fibrosarcoma of the Bone in Dogs

  • Surgical removal of the tumor usually involves a resection of the affected bone
  • Radiation therapy can be attempted as an alternate form of pain relief in very select cases
  • Pain medications
  • Chemotherapy to treat the very rare case of spread of the cancer
  • Home Care

    Your veterinarian will likely prescribe pain medications to assure your dog’s comfort, prior to definitive diagnosis and/or in the aftercare period from surgery.

    You should limit activity of your dog to prevent further pain and to prevent what is called a pathologic fracture, which is an abnormal breaking of the bone due to weakening by cancer, prior to definitive therapy. Your pet should not run, jump or play during this time and you should watch him carefully or help him when climbing stairs or getting in and out of the car.

    Any unexplained bump, lameness or problems with your pet’s mouth should be promptly evaluated by your veterinarian. Most forms of lameness are likely to be associated with arthritis or injury to ligaments and tendons. Likewise, most problems with your pet’s mouth are related to tooth decay and gum disease rather than cancer. But if your dog is not getting better with rest, anti-inflammatory drugs or treatment of bad teeth, than radiographs of the affected body part should be taken to rule-out bone cancer.

    If fibrosarcoma occurs in an area of the body that can be completely removed with surgery, the prognosis can be good for 1 to 2 years or more, as it is a type of cancer that rarely spreads.

    In-depth Information on Canine Bone Fibrosarcoma

    Fibrosarcoma is an uncommon type of cancer to affect the bone. They arise as masses in the mouth more commonly than in the legs. They are often very difficult to distinguish from the more common bone cancer osteosarcoma when small biopsy samples are evaluated. Understandably, this is an important distinction as treatment and prognosis vary drastically for these two cancers. It often requires a larger sample of the tumor to be submitted for a pathologist to make this determination.

    Related Symptoms or Diseases

  • Lameness. This is a general term used to describe pain or discomfort experienced by your pet when moving normally or during minimal exercise. It can be due to arthritis, ligament or tendon tears, or injury to the cartilage cushioning between bones in the joints. These are generally orthopedic injuries that can be corrected with rest, anti-inflammatory drugs, and surgery in select conditions. Lameness however is a cardinal sign of fibrosarcoma and warrants further investigation if your pet is experiencing lameness for which a cause cannot be determined.
  • Fractures. Broken bones are often the result of trauma, but fractures can also occur in bones that have been weakened by cancer. These are called pathologic fractures. Sometimes it is difficult to see the cancer on an X-ray, but it can be the cause of a fracture. If your pet experiences a fracture with minimal trauma, pathologic fracture should be suspected. Your veterinarian should biopsy this type of fracture to determine if cancer is present.
  • Osteomyelitis. An infection in the bone is an uncommon disease that occurs as a result of infectious organisms, such as bacteria or fungi, getting into a bone. This most commonly occurs though an open wound, an open fracture or very uncommonly through a blood borne infection. Osteomyelitis has as a proliferative (fuzzy) mass-like lesion on an X-ray and a biopsy and culture needs to be performed to confirm the presence of infection. This is important, as a rule-out for bone cancer can also have a proliferative appearance on X-rays.
  • Bone infarction. This is a very rare condition in which a blood clot blocks the supply of blood to a bone resulting in death of the bone. This appears as a lytic lesion (loss of bone) on an X-ray, which is an appearance that bone cancer can have as well.
  • Other cancers that affect bone. Other types of cancers arise from the tissues associated with the bone and can mimic fibrosarcoma. These include chondrosarcoma (cancer that arises from cartilage), osteosarcoma (cancer that arises from the bone itself), synovial cell sarcoma (cancer that arises from the cells that line the joints), and hemangiosarcoma (cancer that arises from the blood vessels). Except for fibrosarcoma, these cancers are far less common.

    Very rarely a bone cancer could be due to the metastasis (spread) of cancer from a primary cancer elsewhere in your pet. The most common types of cancer that spread to bone are mammary gland cancer, prostate cancer, urinary bladder cancer, multiple myeloma and lymphosarcoma. These cancers tend to have a distinctively different appearance on X-rays that tips off their presence but still require a biopsy to definitively diagnose them. It is important to distinguish this latter group of metastatic cancers to bone, as the approach to treatment is much different and involves finding out where the primary cancer is in the body.

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